1. Field of the Invention
The present invention relates to a liquid ejection head, an image forming apparatus, and a method of manufacturing a liquid ejection head, and more particularly, to technology for disposing the driving wires of piezoelectric elements provided in a liquid ejection head.
2. Description of the Related Art
There are inkjet type image forming apparatuses comprising print heads (liquid ejection heads) in which nozzles are arranged in a matrix array (see, for example, Japanese Patent Application Publication Nos. 2001-334661 and 2002-166543). The print heads disclosed in Japanese Patent Application Publication Nos. 2001-334661 and 2002-166543 have a common liquid chamber formed on the same side of the pressure chambers as the side on which the nozzles are formed. In these print heads, if drive wires for driving the piezoelectric elements are disposed on the diaphragm, there is a probability that insufficient space is available for laying the drive wires, and high density arrangement of the nozzles becomes difficult. Furthermore, due to restrictions on the size of the common liquid chamber and the complexity of the flow channels between the common liquid chamber and the pressure chambers, the resulting structure makes it difficult to improve refilling performance.
Therefore, various compositions that are different to the aforementioned print heads have been proposed (see, for example, Japanese Patent Application Publication Nos. 9-226114, 2001-179973, 2000-127379, 2003-512211 and 2000-289201). Japanese Patent Application Publication Nos. 9-226114, 2001-179973, 2000-127379 and 2003-512211 disclose compositions where a common liquid chamber and piezoelectric elements are disposed on the opposite side of the pressure chambers from the side on which the nozzles are formed, and Japanese Patent Application Publication No. 2000-289201 discloses a composition where a common liquid chamber and piezoelectric elements are disposed on the same side of the pressure chambers as the side on which the nozzles are formed. The specific composition of each of these print heads is as described below.
Japanese Patent Application Publication No. 9-226114 discloses a composition in which ink supply channels for supplying ink to the pressure chambers are provided on a diaphragm forming the upper surface of the pressure chambers, and a reservoir (common liquid chamber) is formed on the surface of the diaphragm reverse to the surface adjacent to the pressure chambers, in such a manner that ink is supplied from the reservoir to the pressure chambers, through the ink supply channels. However, in this print head, if the drive wires of the piezoelectric elements are arranged on the diaphragm, then as the number of piezoelectric elements on the diaphragm rises with increase in the number of nozzles, there is a probability that insufficient wiring space is available for the drive wires.
Japanese Patent Application Publication No. 2001-179973 discloses a composition in which supply restrictors are provided in a diaphragm, an ink supply tank forming an ink supply unit is provided on the opposite side of the piezoelectric elements from the pressure chambers, and ink supply ports connecting to the pressure chambers are formed passing through the diaphragm, from the ink supply tank. A hermetic sealing cover for ensuring the insulating properties of the piezoelectric elements, and a thin section for absorbing pressure variations in the pressure chambers are formed in the ink supply unit. However, this print head adopts a composition in which a flexible cable is connected to an extending section of the diaphragm, and therefore, the drive wires of the piezoelectric elements must be disposed on the diaphragm, and similarly to Japanese Patent Application Publication No. 9-226114, there is a probability that insufficient wiring space is available for the drive wires.
Japanese Patent Application Publication No. 2000-127379 discloses a composition in which piezoelectric elements are provided on the surfaces of the pressure chambers opposite to the surfaces on which nozzles are provided, a portion of a reservoir for supplying ink is provided on the side adjacent to the piezoelectric elements, and a covering is provided on the piezoelectric elements, in such a manner that electrodes can be extracted by wire bonding, thin film formation, or the like. However, in this print head, the nozzle arrangement has one nozzle row rather than a matrix structure, and is therefore unsuitable for achieving high nozzle density.
Japanese Patent Application Publication No. 2003-512211 discloses a composition in which a porous member having a large number of small, internally connected pores, such as sintered stainless steel, is used as an ink supply layer. However, in this print head, the drive wires of the piezoelectric elements are formed so as to rise up in a direction substantially perpendicular to the diaphragm, until reaching a wiring layer, and a common liquid chamber is provided on top of the wiring layer. Therefore, the flow channel for supplying ink from the common liquid chamber to the pressure chambers is long, and furthermore, since the ink supply layer is constituted by a porous member, the flow channel resistance is high and refilling performance is not satisfactory. Consequently, it is difficult to eject ink of high viscosity or to drive nozzles at a high frequency.
Japanese Patent Application Publication No. 2000-289201 discloses a print head having a composition in which a common liquid chamber and piezoelectric elements are disposed on the same side of the pressure chambers as the side on which the nozzles are formed, the piezoelectric elements disposed on the nozzle surface side of the pressure chambers, and the drive circuit disposed on the opposite side from same being electrically connected by means of aluminum plugs which pass through the laminated layers. However, in this print head, a common liquid chamber is disposed on the same side of the pressure chambers as the side where the nozzles are formed, and hence this composition places restrictions on the size of the common liquid chamber as in the case of the print head disclosed in Japanese Patent Application Publication Nos. 2001-334661 and 2002-166543, and makes it difficult to improve refilling performance. Moreover, while the piezoelectric elements are disposed on the same side of the pressure chambers as the side where the nozzles are formed, the drive circuit for the piezoelectric elements is positioned on the opposite side of the pressure chambers from the side where the nozzles are formed, and therefore the drive wires for the piezoelectric elements must be provided so as to pass through the laminated plates which constitute the pressure chambers. Consequently, if the number of pressure chambers rises with increase in the density of the nozzles, then there is a probability that insufficient wiring space is available for the drive wires.
In print heads in the related art as described above, it is difficult to ensure wiring space for the drive wires, or to improve refilling performance, and it is difficult to achieve high-density arrangement of the nozzles or ejection of high-viscosity ink. Furthermore, since the number of drive wires rises as the nozzle density is increased, then it becomes necessary not only to ensure sufficient wiring space for the drive wires, but also to improve the productivity of the constituent members, including the drive wires. Moreover, depending on the arrangement of the drive wires, it may also be required to provide reliable insulation processing for the drive wires.